Editing Thermal Emission Imaging System (section)

== Discovery of a variety of rocks ==
THEMIS found a wide range of igneous rocks and minerals.  Some of the rocks were low-silica [[basalts]], high silica [[dacite]], [[olivine]] basalts, ultramafic (picritic) basalts, and quartz-bearing granitoid rocks. The olivine basalts were present in a variety of locations, such as on crater floors and in some canyon wall layers. The mineral olivine is important because it is common in more primitive [[magma]]s from the [[Mantle (geology)|mantle]] and it weathers quickly when moisture is present. So, if olivine is present, the climate must have been dry since the time that olivine was exposed. [[Quartz]]-bearing rocks were found in the central uplifts in craters. Rocks in the central uplifts{{Clarify|reason=What central uplifts are these?|date=August 2020}} were probably once buried several kilometers beneath the surface, but raised by the impact process. Rocks of dacite composition show that, within magma chambers, fractional crystallization occurred.<ref>Christensen, P. et al.  2005.  Evidence for magmatic evolution and diversity on Mars from infrared observations.  Nature: 436.  504–509.</ref> In this process, some minerals form crystals, then settle to the bottom of the chamber. Having a variety of rocks increases the chances that some useful/valuable minerals may be found on Mars.